An image forming apparatus (such as a copying machine and a printer) which forms an image by means of an electrophotographic printing method has the following feature: when toner, which is contained in a developing tank and which makes visible an electrostatic latent image formed on a surface of a photoreceptor drum, is consumed and reduced in its amount, toner is supplied from a toner cartridge to the developing tank. For example, when two-component toner including toner and carrier is used, toner contained in a toner cartridge is supplied to a developing tank so that a toner density in toner in the developing tank is not less than a predetermined value. The toner cartridge is detachably and attachably arranged to a predetermined position in the image forming apparatus. When a toner cartridge which is attached to the image forming apparatus runs out of toner, the toner cartridge is exchanged with another.
The electrophotographic printing method in the image forming apparatus encompasses various kinds of methods such as a positive charging method and a reverse charging method. There are many types of toner having different characteristics for respective methods. Also, the type of toner is predetermined for each model of image forming apparatus.
An exchange of a toner cartridge is mostly carried out by a user. When a plurality of image forming apparatuses of different models are closely provided one to another, there is a possibility that a toner cartridge prepared for one model of the image forming apparatuses is attached to another model of the image forming apparatuses by mistake. Especially in image forming apparatuses of the same manufacturer, toner cartridges having the same shape often contain toner of different characteristics. In cases where a plurality of image forming apparatuses of different types closely provided one to another are thus of the same manufacturer, a user easily makes a mistake and attaches a wrong toner cartridge in an exchange.
In light of this, there has been known a conventional image forming apparatus in which, in a toner cartridge, an information storage section for storing inherent information such as a toner characteristic is provided. With this arrangement, it is possible (i) to judge and display whether or not an attached toner cartridge is suitable based on information which is read out from an information storage section by an information processing device provided on the image forming apparatus side (Japanese Unexamined Patent Application Publication, Tokukaihei, No. 2-296259 (published on Dec. 6, 1990)); (ii) to inform remaining amount of toner to a user so that a toner cartridge does not run out of toner suddenly (Japanese Unexamined Patent Application Publication, Tokukaihei, No. 9-134098 (published on May 20, 1997)).
The conventional image forming apparatus, however, has the following problem: when a toner cartridge is suddenly detached from the image forming apparatus during a communication between an information storage section and an information processing device, such a communication is interrupted, thereby causing a communication error. This will cause the following problem. For example, in a case where a toner end of a toner cartridge is determined in accordance with the number of rotations of a motor, the main body of an image forming apparatus transmits the number of rotations of the motor to an IC chip. Therefore, if the communication between the information storage section and the information processing device is interrupted, then the IC chip will have wrong information about the number of rotations of the motor. This will cause a timing of a toner end to be inaccurate. As a result, the following problems will occur: (i) even when it is judged to be a toner end, a large amount of toner still remains in a cartridge; (ii) even when toner in a cartridge runs out, it is not judged to be a toner end.